Low-temperature (<= 300 degrees C) formation of orientation-controlled large-grain (>= 10 mu m) Ge-rich (>= 50%) SiGe crystals on insulator are realized by the gold-induced layer-exchange technique. Stacked structures of a-Si1-xGex (0 <= x <= 1)/Au/SiO2 are employed as starting materials. Here, thin-Al2O3 layers are introduced as diffusion barrier at a-SiGe/Au interfaces to suppress random bulk-nucleation and make (111)-oriented interface-nucleation on SiO2 dominant. For samples with Ge fraction of 80%-100%, (111)-oriented large-grains (>= 10 mu m) are obtained through layer-exchange during annealing at 250 degrees C. On the other hand, layer-exchange for Ge fraction of 50% does not proceed at 250 degrees C. This phenomenon is attributed to retardation of lateral growth by introduction of Si. To enhance lateral growth, increase of annealing temperature is examined. As a result, (111)-oriented large-grains (>= 10 mu m) are realized for SiGe with Ge fraction of 50%-100%, having uniform composition profiles, by annealing at 300 degrees C. This technique is very useful to realize high-performance flexible electronics, employing plastic substrates (softening temperature: similar to 350 degrees C). (C) 2015 Elsevier B. V. All rights reserved.